The present invention relates to a unit for generating, maintaining and eliminating a vacuum and for generating, maintaining and eliminating pressure in, e.g., a tank for collecting and further transporting waste in a vacuum toilet. The invention also relates to a system that includes a vacuum unit constructed in accordance with the invention.
Vacuum ejectors that work in accordance with the so-called Venturi principle are known to the art and are used to generate a sub-pressure, e.g., in a tank connected thereto. By vacuum is meant in this context the state of a gas whose particle density is less than the particle density of the atmosphere at the surface of the earth. The state of a gas can also be designated as a vacuum state when its pressure is lower than atmospheric pressure (DIN 28 400). Such ejectors can be used to generate a vacuum that can typically reach 10-kilopascal (xe2x88x920.9 bar, 90% vacuum).
When such an ejector in a vacuum unit is coupled in a system that includes a tank and compressed-air conduits for the purpose of generating both pressure conditions and vacuum conditions a large quantity of auxiliary material is normally required for fitting and coupling together the system components. A conventional ejector cannot be used in such coupling systems without providing a relatively large number of additional devices, particularly in respect of a vacuum toilet system.
Swedish Patent Specification 502 345 C2 teaches a vacuum unit in which all desired functions have been integrated. The number of parts and ducts or conduits included in the unit, however, is relatively large, which results in undesirable production costs.
Accordingly, one object of the present invention is to eliminate the aforesaid problems by providing a vacuum unit of the kind described in the introduction that includes fewer components and conduits than known vacuum units.
Another object of the present invention is to provide a vacuum toilet system that includes such a vacuum unit.
The present invention is based on the insight that the aforesaid objects can be achieved with a vacuum unit in which an ejector is used to generate both an overpressure and a sub-pressure, by respectively blocking and opening the outlet duct of the ejector.
Thus, an inventive vacuum unit includes a first valve which can be connected to a compressed air source and which has a closed first position and an open second position, a second valve which can be connected to a compressed air source, an ejector that includes an inlet nozzle, an outlet nozzle and a vacuum opening and that is connected to the first valve via said inlet nozzle and to a first connection of the vacuum unit via said vacuum opening, and a piston valve that includes a first inlet, a second inlet and an outlet and that has an open position in which the outlet connects with the first inlet, and a closed position in which the outlet is not connected to the first inlet and the second inlet, and in which piston valve the first inlet is connected to the ejector outlet nozzle, the second inlet is connected to the second valve, and the outlet is connected to a second connection of said vacuum unit, wherein said unit is characterised in that the second valve has a first position in which the second inlet of the piston valve connects with the surroundings, and a second position in which the second inlet of said piston valve communicates with the compressed air source, wherein the piston valve is adjusted to an open position with the second valve in its first position, whereby when the first valve is open there is generated a sub-pressure in the vacuum opening and the piston valve is adjusted to its closed position with the second valve in said second position, whereby opening of the first valve generates an overpressure in the vacuum opening.
This construction provides a vacuum unit that has fewer component parts and ducts or conduits than earlier units of this kind.
The invention also relates to a vacuum toilet system that includes such a vacuum unit.
Other preferred embodiments will be apparent from the dependent claims.